In well drilling operations, a power tong is used to grip and rotate lengths of pipes, rods or other axially elongated bodies for the purpose of connecting together or disconnecting threaded end sections of such bodies. In the usual case, the tong is of the open-headed type having a housing with a central opening and an outward-open passageway or throat which permit the tong to be positioned around a pipe joint without the necessity of lowering the tong over a length of pipe.
When the tong is operated, pipe-gripping means (often referred to as jaws) are caused to revolve around the aforesaid central opening, these jaws causing the pipe or axially elongated object being gripped thereby to axially rotate. Looking at the gripping action of the jaws in more detail, most tongs accomplish the grip by means of a rotor which forces a cam which is attached to the jaw frame to lock into position against a cam surface along the inside surface of the rotor. The action of the cam against the cam surface forces the jaw radially or pivotally radially inward causing a die assembly to engage the pipe. The smaller the cam angle the greater the gripping force produced; however, reduced cam angles can often lead to forces which will deform the pipe. In prior tongs, many attempts to reduce the cam angle have failed because it was not possible to effectively limit the camming angle reduction. Since the range of variance of the cam angle which can be practically used is small, jaw assemblies have very limited ranges of pipe radii that they can be used upon. Accordingly, an object of the present invention is to provide a jaw assembly and a power tong incorporating the same with a primary and a secondary camming function which permits a reduced angle for the primary camming function; thereby increasing grip and decreasing slippage.
Another object of this invention is to provide a jaw assembly and a power tong incorporating the same which allows the cam angle of the primary camming function to be reduced, however, limiting the reduction and preventing damage to pipe or similar axially elongated objects.
Yet another object of this invention is to provide a jaw assembly and a power tong incorporating the same which allows the jaw assembly to be used for a greater range of pipes or similar cylindrical objects, therefore saving time and money from unneeded changes in equipment mandated by different pipe sizes.
These together with other objects and advantages of the invention will become more apparent upon reading the undergoing specification and claims.